In /etc/postfix/main.cf, list the remote site name or address
in the
debug_peer_list parameter. For example, in order to make
the software log a lot of information to the syslog daemon for
connections from or to the loopback interface:
/etc/postfix/main.cf:
debug_peer_list = 127.0.0.1
You can specify one or more hosts, domains, addresses or
net/masks. To make the change effective immediately, execute the
command "postfix reload".
